The field of this invention related to equalizing valves mounted in ninety degree rotatable closure members, known as flappers, and more particularly to biasing systems to keep such equalizing valves in a closed position.
Typically, a well completion includes a sub-surface safety valve. This valve is actuated from the surface using a hydraulic control system with control lines running from the surface to the valve location. These valves feature a closure member which is rotatable through an arc of ninety degrees. The control system pressure is used to move a hollow tube, known as a flow tube, downwardly, usually against a return spring. The downward movement of the flow tube rotates the flapper downwardly and out of the way to allow flow from the producing formation to reach the surface through the flow tube. Removal of pressure from the control system allowed the return spring to bias the flow tube upward, whereupon another spring on the flapper urged it to the closed position, blocking the opening in the flow tube.
With the flapper in the closed position, formation pressure builds up on the closed flapper. In this intended mode of operation, the flapper holds back the flow from the formation in order to allow for safe well operation. The problem that arises occurs when the well needs to be placed in service at a later time. The flapper must then be opened. However, at this time there may be substantial differential pressure acting on substantially the entire cross-sectional area of the flapper. Aggravating this differential pressure problem would be a situation in the well bore above the closed flapper where thousands of feet of the tubing was gas filled or filled with a light density fluid. The presence of gas or light weight fluids above the flapper had, in the past, required that such fluids be replaced with heavier fluid to eliminate or reduce differential pressure across the flapper prior to actuation of the flow tube. The fluid replacement procedure was costly as well as time consuming and better methods were developed to expedite the re-opening of the flapper under conditions of high differential pressure.
The equalizing valve in the flapper design was developed to addressed this issue. This prior art design is illustrated in FIG. 1. A flapper 10 is shown in perspective with a vertical segment 12 machined out adjacent an edge 14. Undercuts 16 and 18 straddle the vertical segment 12 to allow for placement of a leaf spring 20 therein. Leaf spring 20 straddles bore 22 in which is disposed a plunger 24. Plunger 24 has a taper 26 which is biased against a mating edge or surface in bore 22. The plunger 24 is situated so that a flow tube(not shown), when urged downwardly by a control system will first contact plunger 24 and move it against the bias of leaf spring 20. Thus, before the flapper 10 begins to move, the taper 26 has come off of its mating edge or surface in the bore 22 to equalize pressure on the flapper 10. Those skilled in the art will appreciate that the view in FIG. 1 illustrates the down hole side of the flapper and that the flow tube is positioned on the opposite side of the flapper from which location it can make initial contact with the extending plunger 24.
There was a weakness in the design described above which, in some cases, resulted in leakage past taper 26 and its mating surface in bore 22. The reason this happened is directly related to the amount of the flapper 10 that had to be machined away to form the removed vertical segment 12 and its adjacent undercuts 16 and 18. The removal of so much metal to accommodate the leaf spring 20 weakened the flapper 10 sufficiently to allow distortion of bore 22 with resulting leakage past taper 26.
Accordingly, the objective of the present invention is to improve the design of the prior art FIG. 1 so as to eliminate the leakage problem under conditions of high differential pressure across the flapper 10. This and other advantages will become apparent to those skilled in the art from a review of the preferred embodiment, described below.
Relevant to the present invention are U.S. Pat. Nos. 6,079,947; 5,884,705; 5,503,229; and 5,752,569.
An equalizer valve for a flapper in a subsurface safety valve is described. A tapered plunger is biased by compact spring disposed in the plunger bore. The spring is supported by a retaining ring which may be a C-shaped ring extending into a peripheral groove around the plunger bore.